The pH to concentration calculator converts between pH and hydrogen ion concentration [H⁺] using pH = −log₁₀[H⁺]. Enter pH to find [H⁺], or enter [H⁺] to find pH. Also calculates pOH and [OH⁻] at 25°C.
pH ↔ Concentration Calculator
How to Use the pH to Concentration Calculator
This calculator converts between pH and hydrogen ion concentration using the fundamental relationship pH = −log₁₀[H⁺].
From pH to [H⁺]
Enter a pH value (0-14). The calculator finds [H⁺] = 10^(-pH). pH 4 → [H⁺] = 10⁻⁴ = 0.0001 mol/L. pH 7 → [H⁺] = 10⁻⁷ = 0.0000001 mol/L. Each pH unit = 10× difference in [H⁺].
From [H⁺] to pH
Enter concentration in mol/L, mmol/L, or nmol/L. pH = −log₁₀[H⁺]. For [H⁺] = 3.162 × 10⁻⁵ mol/L: pH = −log(3.162 × 10⁻⁵) = 4.5.
pOH and [OH⁻]
At 25°C, pH + pOH = 14. pOH = 14 − pH. [OH⁻] = 10^(−pOH). A solution with pH 4 has pOH = 10 and [OH⁻] = 10⁻¹⁰ mol/L.
FAQ
What is the pH formula?
pH = -log₁₀[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. Rearranging: [H⁺] = 10^(-pH). At 25°C, a neutral solution has pH = 7 and [H⁺] = 10⁻⁷ mol/L. Acids have pH < 7 (higher [H⁺]), bases have pH > 7 (lower [H⁺]).
What is the relationship between pH and pOH?
At 25°C, pH + pOH = 14 (the ionic product of water Kw = 10⁻¹⁴). So pOH = 14 - pH and [OH⁻] = 10^(-pOH). A solution with pH 4 has pOH = 10 and [OH⁻] = 10⁻¹⁰ mol/L.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
What pH do common substances have?
Stomach acid: pH 1-2. Vinegar: pH 2-3. Coffee: pH 5. Pure water: pH 7. Blood: pH 7.35-7.45. Baking soda: pH 8.3. Bleach: pH 11-13. Drain cleaner: pH 13-14. Each unit change represents a 10-fold change in [H⁺] concentration.